Yu Hirano

A competitive immunochromatographic assay for testosterone based on electrochemical detection

An immunochromatographic assay using nitrocellulose membrane was combined with electrochemical detection using an electrode chip in order to quantitatively detect testosterone as a model analyte. The electrode chip consisted of a gold working electrode, a counter electrode and a pseudo-reference electrode, all fabricated on the bottom of a 3.2mmx3.2mm well. Competitive immunoreactions on the membrane were initiated by flowing a solution containing testosterone and horseradish peroxidase (HRP)-labeled testosterone (a competitor) over the membrane. Prepared membrane was placed in a solution containing ferrocenemethanol (FcOH) and H(2)O(2) in the well of the electrode chip, and the enzyme reaction was detected by amperometry. Labeled HRP captured on the membrane catalyzed the oxidation of FcOH to the oxidized form FcOH(+), which was reduced electrochemically by the electrode chip. The electrochemical response of the reduction current decreased with increasing concentration of testosterone over the range 1-625ng/ml.

Imaging of enzyme activity by scanning electrochemical microscope equipped with a feedback control for substrate–probe distance

The enzymatic activity of diaphorase (Dp) immobilized on a solid substrate was characterized using a scanning electrochemical microscope (SECM) with shear force feedback to control the substrate-probe distance. The shear force between the substrate and the probe was monitored with a tuning fork-type quartz crystal and used as the feedback control to set the microelectrode probe close to the substrate surface. The sensitivity and the contrast of the SECM image were improved in the constant distance mode (distance, 50 nm) with the shear force feedback compared to the image in the constant height mode without the feedback. By using this system, the SECM and topographic images of the immobilized diaphorase were simultaneously measured. The microelectrode tip used in this study was ground aslant like a syringe needle in order to obtain the shaper topographic images. This shape was also effective for avoiding the interference during the diffusion of the enzyme substrates.

Construction of Time-Lapse Scanning Electrochemical Microscopy with Temperature Control and Its Application To Evaluate the Preservation Effects of Antifreeze Proteins on Living Cells

Antifreeze proteins (AFPs) can protect cells from hypothermic damage; however, their mechanism of action remains unclear. Scanning electrochemical microscopy (SECM) can evaluate the size and activities of cells, although long-term continuous monitoring has been unsuccessful. We constructed a novel, fully automated, time-lapse SECM system and investigated the cell preservation effect of AFPs by analyzing single cellular topography at low temperatures. From the SECM measurements, mammalian cells (HepG2), treated in Euro-Collins (EC) solution at 4 degrees C, began to swell at 8 h and then immediately ruptured. In AFP-containing EC solution, the cellular size did not change until 16 h and then gradually increased and finally ruptured. In addition, the cellular height at rupture point significantly increased in the presence of AFPs. These results suggest that AFPs stabilize the cellular membrane and protect cells from hypothermic damage. This SECM system allowed us to observe the single cellular response to hypothermia by long-term automatic scanning and will be applicable for analysis to other cellular activities and topographies.

Hypothermic preservation effect on mammalian cells of type III antifreeze proteins from notched-fin eelpout ☆

Antifreeze proteins (AFPs) can bind to the surface of ice crystals and have also been suggested to protect cells from hypothermic damage. The present study reports that type III AFPs from notched-fin eelpout, Zoarces elongatus Kner, can protect cells during hypothermic storage. This fish naturally expresses at least 13 isoforms of type III AFP (denoted NfeAFPs), the primary sequences of which were categorized into SP- and QAE-Sephadex binding groups (SP- and QAE-isoforms). We compared the preservation ability between the extracted isoform mixtures (NfeAFPs) and a recombinant single SP-isoform (RcNfeAFP6). Experiments were performed using cultivated mammalian cells (HepG2) exposed to 4 degrees C for 24-72 h. The preserved cells were evaluated by measuring LDH released, intracellular ATP, and WST-8 reduction. It appeared that the protective effect of the 2 samples increases dose-dependently at concentrations between 2 and 10 mg/ml. Under highest soluble amount of the protein (approximately 10 mg/ml), cell viability significantly improved compared with the ordinary preservation fluid (P<0.01). This effect was larger with NfeAFPs than with RcNfeAFP6 at the same concentration. The successful hypothermic preservation of cells using natural NfeAFPs may have a wide range of applications for cell engineering and clinical medical care.

Interstrand cross-link of DNA by covalently linking a pair of abasic sites

A pair of apurinic/apyrimidinic sites formed in DNA has been covalently connected with bis(aminooxy) derivatives. The efficacy of the interstrand cross-link is associated with the structural tethering of two aminooxy groups. The interstrand cross-link constructed stable DNA scaffolds for enzyme alignment.

Analysis of beat fluctuations and oxygen consumption in cardiomyocytes by scanning electrochemical microscopy

The contractile behavior of cardiomyocytes can be monitored by measuring their action potentials, and the analysis is essential for screening the safety of potential drugs. However, immobilizing cardiac cells on a specific electrode is considerably complicated. In this study, we demonstrate that scanning electrochemical microscopy (SECM) can be used to analyze rapid topographic changes in beating cardiomyocytes in a standard culture dish. Various cardiomyocyte contraction parameters and oxygen consumption based on cell respiration could be determined from SECM data. We also confirmed that cellular changes induced by adding the cardiotonic agent digoxin were conveniently monitored by this SECM system. These results show that SECM can be a potentially powerful tool for use in drug development for cardiovascular diseases.

Development of a scanning electrochemical microscopy-based micropipette and its application to analysis of topographic change of single-cell.

Scanning electrochemical microscopy (SECM) is useful for analyzing various cellular responses. We have combined a micropipette (MP) with SECM to perform quantitative solution delivery to single cells. In this system, since the concentrations of electrochemical mediators are changed by the volume of solution delivered from the MP, we constructed a feedback control system to regulate MP delivery by SECM-detected signals. Cellular responses induced by MP delivery could be monitored by the SECM, and cell apoptosis was successfully detected by adding a kinase inhibitor of two orders of magnitude less than what is required in the conventional method. The SECM-based MP can activate a target cell, requiring a minimal amount of agent, and can continually examine target cell responses. This system improves the accuracy of delivery from the MP and is useful for single-cell analysis.

The obligate alkaliphile Bacillus clarkii K24-1U retains extruded protons at the beginning of respiration

Alkaliphiles grow under alkaline conditions that might be disadvantageous for the transmembrane pH gradient (ΔpH, outside acidic). In this study, the behaviors of extruded protons by the respiration of obligate alkaliphilic Bacillus clarkii K24-1U were investigated by comparison with those of neutralophilic Bacillus subtilis IAM 1026. Although whole-cell suspensions of both Bacillus species consumed oxygen immediately after the addition of air, there were lag times before the suspensions were acidified. Under alkaline conditions, the lag time for B. clarkii significantly increased, whereas that for B. subtilis decreased. In the presence of valinomycin or ETH-157, which disrupts the membrane electrical potential (Δψ), the cell suspensions of both Bacillus species acidified immediately after the addition of air. Artificial electroneutral antiporters (nigericin and monensin) that eliminate the ΔpH exhibited no significant effect on the lag times of the two Bacillus species except that monensin increased the lag times of B. clarkii. The inhibition of ATPase and the Na+ channel also exhibited little effects on the lag times. The increased lag time for B. clarkii may represent the Δψ-dependent proton retention on the outer surface of the cytoplasmic membrane to generate a sufficient ΔpH under alkaline conditions.

Bienzyme reactions on cross-linked DNA scaffolds for electrochemical analysis.

Enzymes play an essential role in various detection technologies. We show here that interstrand cross-linked oligodeoxynucleotides (CL-ODNs) can provide stable scaffolds for efficiently coupling two types of enzymatic reactions on an electrode. Glucose can be electrochemically detected using glucose oxidase (GOx) and horseradish peroxidase (HRP). When both GOx and HRP were immobilized on an electrode surface by attachment at the termini of CL-ODNs, the current value was markedly increased compared with that obtained on a standard ODN scaffold. The relative orientation of the enzymes on the electrode strongly affected the current intensities. The CL-ODN also allowed GOx-HRP to form a complex on the tiny surface of a microelectrode, resulting in the imaging of local glucose distribution. These results suggest that CL-ODNs have potential utility in other sensing technologies.

Function Control of Anti-microRNA Oligonucleotides Using Interstrand Cross-Linked Duplexes

MicroRNA (miRNA)-guided argonaute (Ago) controls gene expression upon binding to the 3′ UTR of mRNA. The miRNA function can be competitively inhibited by single-stranded anti-miRNA oligonucleotides (AMOs). In this study, we constructed a novel type of AMO flanked by interstrand cross-linked 2′-O-methylated RNA duplexes (CLs) that confer a stable helical conformation. Compared with other structured AMOs, AMO flanked by CLs at the 5′ and 3′ termini exhibited much higher inhibitory activity in cells. Anti-miRNA activity, nuclease resistance, and miRNA modification pattern distinctly differed according to the CL-connected positions in AMOs. Moreover, we found that the 3′-side CL improves nuclease resistance, whereas the 5′-side CL contributes to stable binding with miRNA in Ago upon interaction with the 3′ part of miRNA. These structure-function relationship analyses of AMOs provide important insights into the function control of Ago-miRNA complexes, which will be useful for basic miRNA research as well as for determining therapeutic applications of AMO.